Apparatus for the cooling of solid residues of gasification

ABSTRACT

The present specification describes and claims a method and apparatus for use in cooling the solid residue of gasification of a reactor operated at a pressure above atmospheric for the gasification of carbonaceous materials. The residue of gasification is conducted out of the reactor into a cooling apparatus located therebelow and flows through the cooling apparatus from the top to the bottom thereof. A cooling liquid is introduced into the solid residue in the upper region of the cooling apparatus and is metered such that the greater portion of the heat contained in the residue is eliminated in the form of heat of vaporization, sensible heat and chemical binding energy with the resultant steam and reaction products produced. The remaining residual heat which corresponds to the difference between the desired final temperature and the temperature after cooling by the liquid, is eliminated by a gas blown into the bottom region of the cooling apparatus and/or by indirect heat exchange.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of copending applicationSer. No. 104,249, filed Dec. 17, 1979, now U.S. Pat. No. 4,288,294,issued Sept. 8, 1981.

The present invention relates to a method and an apparatus for coolingthe solid residues of gasification of a reactor operated underover-pressure for the gasification of carbonaceous materials, whereinthe residues of gasification are conducted out of the reactor into acooling apparatus located therebelow and flow through the coolingapparatus substantially from the top to the bottom thereof.

Cooling apparatus of this kind form a unit with the reactor with respectto the operating pressure i.e. the operating pressure of the reactorprevails in the cooling apparatus.

In general, it is necessary to cool the solid residues of gasification,which are hereinafter referred to as "residual coke" and which can beentirely of predominantly ash, before they are conducted out of thepressure region, since the handling of the residual coke involves manydifficulties and the plants and transportation means coming into contactwith the hot residual coke would also be subjected to considerablestresses. Normally, a temperature in the order of magnitude of 250° to200° C. upon leaving the cooling apparatus will be sufficiently low.Thus, a considerable cooling capacity is required if the initialtemperature of the residual coke lies at, for example, 900° to 1000° C.upon leaving the reactor and entering the cooling apparatus.

It is desirable for the cooling apparatus to have a large throughputcapacity and a large cooling capacity and to keep it physically as smallas possible, particularly to ensure that the overall height of theentire apparatus forming part of the pressure region is notsubstantially greater than it has to be, taking into account, forexample, the requirements relating to the reactor.

The most obvious possibility is that of cooling the residual cokeexclusively by quenching by means of water, although this alwaysinvolves considerable difficulties if special precautions are not taken.Thus, in the event of too great a quantity of water, residual moisturecan remain in the coke and can possibly be present in such a quantitythat the residual coke and the water together form a cake or evensludge. It has to be taken into account that the granular size of theresidual coke will generally be fine to very fine, for example in theorder of magnitude of 0 to 5 mm. In the case of wet residual coke, thereis the risk that it will cake on the walls of the cooling apparatus, sothat the cross section of the passage through the cooling apparatus isreduced and might even be reduced to zero, with the result that thecooling apparatus will be clogged. Since the cooling apparatus and thereactor form an operating unit, it has to be taken into account that anyfault or trouble in the cooling apparatus necessarily leads to a faultor an interruption in the operation of the reactor. The use of too largea quantity of cooling liquid necessarily leads to a corresponding largequantity of steam which, since it flows into the reactor, can impair thegasification process in the reactor, at least in certain cases. Thisapplies in the case of, for example, hydro-gasification in which theother gases contained in the hydrogen should, in general, be as few aspossible. It will be appreciated that the hydrogen used as agasification agent cannot be 100% hydrogen in practical operation, sincethe residual moisture in the coal to be gasified always itself leads tothe formation of steam and thus to the production of CO and CO₂.However, in general, it will be desirable to minimise the steam contentin such cases.

An aim of the present invention is, inter alia, to develop a method andan apparatus of the kind described initially, such that the solidresidues of the gasification process taking place in the reactor can berapidly and inexpensively cooled to a temperature at which the residualcoke can be readily handled and which does not over stress the devicesfor receiving and transporting the residual coke. The gasificationprocess should not be impaired either directly or indirectly to anygreat extent by the steps of the method necessary for the coolingoperations. It is to be ensured in all cases that the cooled residualcoke can be removed from the pressure region in a state in which it doesnot contain any moisture, or only such small quantities of moisture thatits ability to flow within the cooling apparatus is not impaired. Theresidual coke should under all circumstances flow through the coolingapparatus in a trouble-free manner at the desired rate.

According to the present invention there is provided a method of coolingthe solid residues of gasification of a reactor operated underover-pressure for the gasification of carbonaceous materials, whereinthe residues of gasification are conducted out of the reactor into acooling apparatus located therebelow and flow through the coolingapparatus from the top to the bottom thereof, cooling liquid beingintroduced into the solid residues of gasification in the upper regionof the cooling apparatus and being metered such that the greater portionof the heat contained in the residues is eliminated in the form of heatof vaporization and sensible heat and chemical binding energy with theresultant steam and the reaction products produced, and the remainingresidual quantity of heat, which corresponds to the difference betweenthe desired final temperature and the temperature after cooling by theliquid, is eliminated by gas which is blown into the bottom region ofthe cooling apparatus and/or by indirect heat exchange.

It is advantageous to regulate the quantity of cooling gas to be fed independence upon the temperature monitored by a temperature sensorprovided at a suitable location. Advantageously, the quantity of coolingliquid which is admitted is regulated in dependence upon the temperatureof the residue of gasification by means of a temperature sensor which islocated in the direction of flow of the said residues at such a distancedownstream of the location at which the liquid is admitted that adequatecooling is effected on the one hand and, on the other hand, atroublesome residual water content of the coke is avoided. It has provedto be advantageous to eliminate in this manner 75% of the total heat tobe dissipated.

The method in accordance with the invention can be performed by using anapparatus which is disposed below the reactor and which forms therewitha system subjected to a pressure above atmospheric, a feed line for acooling liquid being provided in the top region of a substantiallychute-like interior space of the cooling apparatus, a temperature sensorbeing disposed downstream of this location in the direction of flow ofthe gasification residues to be cooled, and the bottom region of thecooling apparatus being provided with a feed line for a cooling gas. Itwill be appreciated that the cooling liquid can be fed at a plurality oflocations, for example in the same plane or alternatively, if required,in planes lying one above the other. However, in general it will besufficient to introduce the cooling liquid approximately in the centralregion of the cross-sectional area of the cooling apparatus. Preferablythe cooling apparatus is provided with at least one guide part which isbuilt into the interior space of the cooling apparatus. Each guide partextends for a substantial portion of its length in the direction of flowof the residue gasification. This built-in guide part is intended toprevent the residual coke from moving downwardly only in the centralcross-sectional region and then emerging from the bucket wheel in aninadequately cooled state, whilst the residual coke located in the edgeregion, although adequately cooled, does not move downwardly or onlymoves downwardly slowly. In general, for reasons of saving space, itwill be desirable for this downwardly extending built-in part not tohave too large a cross-section, and the top and bottom of the built-inpart can taper conically in a conventional manner.

The walls defining the said interior space can be at least partially inthe form of a heat exchanger, or can be provided with a heat exchangerwhich, under normal operating conditions, absorbs the remainder of theheat to be eliminated from the coke. If, for some reason or other, thecase should arise in which the coke contains a perceptible moisturecontent down to the central or bottom region of the cooling apparatus asa result of introducing the cooling liquid, the action of these heatexchangers can be reversed such that heat is introduced into theresidual coke in these regions in order to evaporate the water locatedtherein at least to the extent that it does not become troublesomeduring further handling of the residual coke. This reveral of the actionof the heat exchanger will generally be effected automatically since,due to the relatively high temperature of, for example, 200° C. whichthe coke always exhibits upon leaving the cooling apparatus, the mediumflowing through the heat exchanger will, after entering the heatexchangers, also have a relatively high level of temperature which willstill result in a cooling action under normal operating conditions butwhich, with a reversal of the conditions, lies above the level oftemperature of the moist residual coke, in, for example, the bottomregion of the apparatus.

The present invention will now be further described, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section through one embodiment of a systemaccording to the present invention, comprising a reactor and coolingapparatus,

FIG. 2 is a section taken on the line II--II of FIG. 1.

Cooling apparatus II is arranged within a pressure resistant casing 12which is connected to a pressure-resistant casing 14 of a reactor 16,arranged thereabove, for the gasification of carbonaceous materials, andto a casing 18 arranged below the casing 12 and provided with a lockarrangement 20, to form a pressure-resistant system.

The carbonaceous materials to be gasified are fed to the reactor 16 bymeans of a screw conveyor 22. A feed line 24 for the gasification agent,such as hydrogen, is provided below the screw conveyor 22 at a distancetherefrom. A fluidized bed 26 builds up in the bottom portion of thereactor 16 under the action of the upwardly flowing gasification agent.

The solid residues 28 of gasification, which generally still containconsiderable quantities of carbon and are thus hereinafter referred toas "residual coke", accumulate below the fluidized bed 26 and passthrough a passage 30 into the cooling apparatus 11 which is disposedbelow the reactor 16 and whose interior space 32, through which thegasification residues flow downwardly, is defined in part, by a spiralpipe 34. An insert 36, also of hollow cylindrical construction, isdisposed between the pressure-resistant casing 12 and the spiral pipe 34and, together with the casing 12, defines an annular chamber 38 withinwhich is disposed a thermally insulating material such as mineral wool.Adjacent turns of the spiral pipe 34 are interconnected by a continuousweb 40 such that the residual coke to be cooled cannot escape outwardlyfrom the chamber 32 bounded by the inside of the spiral pipe 34.

The spiral pipe 34 is provided with an inlet line 42 and an outlet line44 for a cooling medium and is secured in the top region of the casing12 to a continuous bracket by, for example, welding. The bottom end ofthe spiral pipe 34 is free, that is to say, it is not secured, so thatthe spiral pipe can readily follow changes in length caused byfluctuations in temperature.

A built-in body 48 is disposed coaxially within the spiral pipe 34 andis held in position at a distance therefrom by means (not illustrated inthe drawings) such as radial bars, ribs or the like which are secured tothe webs 40 or to the actual tubes of the spiral pipe 34, such that anannular chamber 32 is created through which the residual coke flowsdownwardly. The built-in body 48 is intended to ensure that the heat isadequately eliminated in the centre of the gasification residues whichare moving slowly downwardly.

The bottom end of the cooling chamber 32 is provided with an outletopening 50 beyond which is disposed a bucket wheel located in a housing52. The bucket wheel performs substantially a metering function, so thatit determines the rate at which the residual coke flows downwardlythrough the chamber 32. Although the dwell time of the residual cokewithin the cooling apparatus depends upon the prevailing conditions,such as entry temperature, cooling performance and outlet temperature,an average dwell time of the individual granules of residual coke of,for example, the order of magnitude of from 5 to 20 minutes willcontinue a realistic value in practical operation.

The cooled residual coke discharged by the bucket wheel 54 enters thecasing 18 and then the pressure lock 20 which substantially comprisestwo spaced shut-off elements 56 and 58 which are alternately opened andclosed in a conventional manner. The region 60 located between the twoelements 56 and 58 is provided with a line 62 through which thenecessary equalisation of pressure is effected. The cooled solidresidues of gasification flow outwardly through the bottom, openedshut-off element 58.

A feed line 64 for a cooling liquid is provided in the top region of thecooling apparatus 11 between the passage 30 and the top end of thebuilt-in body 48. The cooling liquid, preferably water, is introducedthrough the line 64 directly into the top region of the chamber 32 andthus into the residual coke located therein. Thus, direct cooling takesplace. A temperature sensor 68 is disposed at a suitable distance belowthe location or the region 66 in which the cooling liquid is introduced,the temperature sensor 68 being connected to a control 72 of a valve 74by way of a line 70. The control valve 74 is incorporated in the feedline 64. Relatively accurate metering of the quantity of cooling waterrequired at any given time can be achieved by way of the temperaturesensor 68, so that, on the one hand, adequate cooling is effected by adirect method, although, on the other hand, the introduction of toogreat a quantity of liquid is avoided. It is necessary to avoid theintroduction of too great a quantity of liquid as when it is greaterthan that corresponding to the quantity of heat required to beeliminated, this can then lead to difficulties when the residual coke isflowing downwardly through the chamber 32. Under normal operatingconditions, the quantity of coke, the initial temperature and thequantity of water should be matched to one another such that at leastthe greater portion of the water is vaporized or is reacted with thecarbon of the residual coke at the level at which the temperature ismeasured, that is to say, on a level with the temperature sensor 68. Thetemperature maintained in this region should lie in excess of the pointof condensation of the cooling liquid under the conditions at any giventime, that is to say, particularly at the prevailing operating pressure.It will be appreciated that it is possible, and also desirable, tointroduce the cooling liquid into the residual coke so as to be fairlyuniformly distributed over the cross-section of the cooling apparatus.Correspondingly, it is also possible to provide several temperaturesensors 68 below the region or the plane in which the cooling liquid isintroduced. It is only then necessary to determine which of thetemperature sensors or which combination of measured values controls thechamber 32.

There is provided in the bottom region of the cooling apparatus at leastone feed line 76 through which a gaseous cooling medium, which should beas dry as possible, is introduced into the interior space 32 of thecooling apparatus between the bottom end of the spiral pipe 34 and thebucket wheel 54. A smaller portion of the heat in the residual coke iscarried off (also upwardly into the reactor 16) by means of this coolinggas. A further purpose of the cooling gas is to prevent steam,attributable to the cooling liquid introduced through the line 64, fromflowing downwardly into those regions of the cooling apparatus 11 or ofthe chamber 32 in which the residual coke has already been cooled to agreater extent and in which there is thus the risk that the point ofcondensation of the steam will be passed in a negative direction. Thecooling gas fed through the line 76 also leads to the cooling gas beingmixed with the steam, so that the partial pressure of the steam in theresultant mixture of steam and cooling gas is any case lower, and thusthe risk of condensation also decreases.

A further portion of the heat to be eliminated is absorbed by the mediumflowing through the spiral pipe 34. It is thereby quite possible that,in the event of over-metering of cooling liquid leading to the residualcoke being cooled to too great an extent below the point ofcondensation, conditions with respect to the transfer of heat betweenthe residual coke and the spiral pipe 34 will be reversed at least inpartial regions of the cooling apparatus, such that the temperature ofthe cooling medium lies above that of the residual coke and thus heat istransferred to the residual coke with the result that the temperature ofthe residual coke in any case increases to an extent that it lies abovethe point of condensation.

By way of example, if 75% of the total quantity of heat to be eliminatedis removed by the cooling water, approximately 25% (relative to thetotal quantity of heat to be eliminated) is eliminated or dissipated assensible heat by the water or the resultant steam, approximately 25% iseliminated or dissipated in the form of vaporization, and approximately25% is eliminated or dissipated as chemical binding energy with theproducts of reaction produced during the endothermic reaction of waterand gas. With an initial temperature of the residual coke in the orderof magnitude of 700° to 900° C., it may readily be anticipated thatreactions will take place between the steam and the carbon of theresidual coke to form, particularly, CO and H₂. The remaining 25% of theheat is eliminated by the cooling gas introduced through the line 76and/or the cooling medium flowing through the spiral pipe 34.

With an initial temperature of the residual coke of approximately 900°C. after leaving the passage 30, and a final temperature ofapproximately 200° C. upon being discharged from the cooling apparatus11 by the bucket wheel 54, the above-described result will be obtainablewith a water consumption in the order of magnitude of approximately 0.1to 1.5 liters per kilogram of residual coke. This quantity of waterwould correspond to a water content, in the order of magnitude of from 1to 2%, of the starting material, that is to say, the coal introducedinto the reactor 16 by means of the screw conveyor 22. Consequently,although the portion of the cooling water which has not reacted with thecarbon of the residual coke enters the reactor 16 in the form of steam,the reactions themselves taking place in the reactor are not impairedwhen, for example, the coal is to be hydrogasified in the reactor 16.The same also applies to the cooling gas which is fed through the line70 and which can be the gasification agent used in the reactor 16 or,alternatively, some other gas such as CO₂. In order to achieve thedesired aim, that is to say, additional cooling and possibly to avoidthe intrusion of steam into the bottom regions of the cooling apparatus,it will generally be sufficient to introduce small quantities of gasthrough the line 70, unless the residual coke located in the coolingapparatus 11 is to be loosened by the upwardly flowing gas. Thispossibility also lies within the scope of the teaching of the presentinvention.

It has already been mentioned that, during the metering of the coolingwater, it is important that the point of condensation should not bepassed in a negative direction where steam might be present, in order toavoid condensation of the steam. The point of condensation lies atapproximately 290° C. when the entire system is under pressure of, forexample, 80 bar. Consequently, the water has to be metered such that thefinal temperature attained by the cooling action of the water lies a fewdegrees above the point of condensation, that is to say, for example,between 310° and 330° C. These conditions then result in the residualcoke having a quantity of heat which is to be eliminated by the coolinggas and/or by the spiral pipe 34 in order to arrive at the desired finaltemperature of, for example, 200° or 250° C.

It will be appreciated that, when necessary it is possible to providethe outside of the built-in body 48 with a spiral pipe or to constructits outer wall in the form of a spiral pipe.

Further temperature sensors, such as 78 and 80, can be arranged betweenthe upper temperature sensor 68 and the bucket wheel 54 and can serve tomonitor and control the feeding of liquid and gaseous cooling media. Byway of example, it is conceivable to use a temperature sensor, locatedin the bottom region of the cooling apparatus, to control the speed ofrotation of the bucket wheel 54 in dependence upon the temperaturemeasured at any given time, since the rotational speed of the bucketwheel affects the dwell time of the coke in the cooling apparatus, andthe extent of the cooling action is also controllable through the dwelltime.

I claim:
 1. Apparatus for cooling the solid residues of gasificationfrom a reactor operated at a pressure above atmospheric for thegasification of carbonaceous materials, which apparatus is disposedbelow the reactor and, together with the reactor, forms a pressuresystem with the reactor, said apparatus having an upper region and alower region, said upper region of the cooling apparatus beingsubstantially chutelike, at least some of the wall surface of saidapparatus defining a cooling chamber comprising pipes through which aheat exchange medium can flow, elongated guide means positionedcentrally of said cooling chamber and extending in the direction of flowof said residues of gasification substantially the length of saidchamber from said upper region to said lower region, thereby forming anannular passage in said chamber through which said residues flow, saidcooling chamber being provided with a first feed line for introducing acooling liquid directly into said upper region of the cooling apparatusand into the solid residues located therein, a temperature sensordisposed downstream of this location in said upper region in thedirection of flow of the residues of gasification to be cooled, and saidlower region of the cooling apparatus being provided with a second feedline for introducing a gas directly into said lower region of theapparatus.
 2. Apparatus according to claim 1, wherein walls defining achamber in the cooling apparatus through which the solid gasificationresidues flow are at least partially formed by a serpentine pipe heatexchanger.
 3. Apparatus according to claim 2 wherein said serpentinepipe heat exchanger is unsecured at its lower end.
 4. Apparatusaccording to claim 1, wherein said pipes are arranged so as to abutclosely against each other.
 5. Apparatus according to claim 1 whereinsaid pipes are interconnected by webs.